AIM4170 Stray Signal Rejection

This scan of the AM broadcast band (using the Band Scan function) shows several of the strong stations on the north east side of Dallas being picked up on a 20 meter dipole. KRLD runs 50KW and is located about 6 miles from the receiving antenna. This is a scan of the 20 meter dipole itself across the AM band. Notice how the radio stations produce only small glitches in the measured resistance and the other parameters. This is a band scan showing the results of connecting a signal generator directly to the RF connector of the analyzer. The generator has a 50 ohm output impedance. It's output was adjusted to produce a signal with a peak value of 150mv at the input to the analyer. This is considerably stronger than the signals from the AM broadcast stations shown above. The impedance of the signal generator can be measured accurately even with a strong signal in the middle of the band. Note the Rs and Rp readings of 50 ohms on the right side of the graph. The green line is the magnitude of the measured impedance. The 1MHz signal disturbs the reading over a range of less than 50KHz.